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CN-121994354-A - Frequency-stabilizing phase-locked mid-infrared single-cavity double-comb measuring system and method

CN121994354ACN 121994354 ACN121994354 ACN 121994354ACN-121994354-A

Abstract

The present invention discloses a frequency stable phase-locked mid infrared single cavity dual comb measurement system and method, which solves the problems of complex system structure and large volume caused by the need for ultra stable external optical/microwave reference, pump broadband servo locking, high-frequency precision electronic control loop, etc. in existing dual comb measurement systems. The present invention adopts a single cavity dual comb architecture with homologous pumping, and combines optical and electrical mixing to eliminate the innovative mechanism of pump frequency and zero frequency offset. Therefore, it does not require complex means such as reference frequency locking, repetition frequency and carrier envelope offset frequency detection required by traditional solutions, and has the advantages of easy construction and easy operation.

Inventors

  • WANG LEIRAN
  • SUN QIBING
  • Ren Dezheng
  • Ming Xianshun
  • ZHANG WENFU
  • ZHAO WEI

Assignees

  • 中国科学院西安光学精密机械研究所

Dates

Publication Date
20260508
Application Date
20260211

Claims (10)

  1. 1. The mid-infrared single-cavity double-comb measuring system with the frequency stabilization phase locking is characterized by comprising a pumping laser unit, a sideband generating unit, a single-cavity double-comb unit, a spectrum monitoring unit, a homodyne extracting unit, a power balancing unit, a double-comb detecting unit and a signal analyzing unit; the pumping laser unit is connected with the input end of the sideband generating unit and is used for emitting mid-infrared pumping laser to the sideband generating unit; The output end of the sideband generating unit is connected with the input end of the single-cavity double-comb unit and is used for carrying out electro-optic modulation on pump laser so as to generate an optical frequency sideband and outputting corresponding light beams to the single-cavity double-comb unit; The single-cavity double-comb unit is used for receiving the light beams output by the sideband generating unit, realizing the frequency comb generation and spectrum expansion of two beams in different propagation directions through a four-wave mixing effect, and then dividing the output corresponding light beams into a monitoring light beam and a testing light beam, wherein the testing light beam is used for inputting an input end of a target to be tested; The spectrum monitoring unit is arranged on the optical path where the monitoring beam is located and is used for monitoring the spectrum characteristics of the monitoring beam; the input end of the homodyne extraction unit is used for connecting with the output end of the target to be detected, and the output end of the homodyne extraction unit is connected with one input end of the double-comb detection unit; The input end of the power balancing unit is used for connecting with the output end of the target to be tested, and the output end of the power balancing unit is connected with the other input end of the double-comb detection unit; the power balancing unit is used for carrying out power balancing on the light beam output by the target to be tested; the output end of the double-comb detection unit is connected with the signal analysis unit and is used for carrying out balance detection on the light beams output by the homodyne extraction unit and the power balance unit so as to eliminate zero frequency offset and realize the conversion of the double combs from optical frequency to radio frequency; the signal analysis unit is used for measuring beat frequency signals of the double combs.
  2. 2. The frequency-stabilized phase-locked mid-infrared single-cavity double-comb measurement system of claim 1, further comprising an amplifying beam-splitting unit; the input end of the amplifying beam splitting unit is used for being connected with the output end of the target to be detected, the first output end of the amplifying beam splitting unit is connected with the input end of the homodyne extraction unit, the second output end of the amplifying beam splitting unit is connected with the input end of the power balancing unit, and the amplifying beam splitting unit is used for amplifying the beam power output by the target to be detected, dividing the beam power into a reference beam and an original beam and outputting the reference beam and the original beam to the homodyne extraction unit and the power balancing unit respectively.
  3. 3. The frequency-stabilized phase-locked mid-infrared single-cavity double-comb measuring system according to claim 2, wherein the pump laser unit is a single-frequency laser (1); The sideband generation unit comprises an electro-optic modulator (2) and a microwave generator (3); The output end of the single-frequency laser (1) is connected with the optical input end of the electro-optic modulator (2), and the line width is smaller than 100MHz and the power is larger than 20mW; the optical output end of the electro-optical modulator (2) is connected with the input end of the single-cavity double-comb unit; the microwave generator (3) is connected with the electrical input end of the electro-optic modulator (2).
  4. 4. The frequency-stabilized phase-locked mid-infrared single-cavity double-comb measurement system as claimed in claim 3, wherein the single-cavity double-comb unit comprises an input waveguide (41), an upper arm waveguide (42), a lower arm waveguide (43), an output waveguide (44), a micro-ring cavity waveguide (45) and a first beam splitter (5); the input end of the input waveguide (41) is connected with the optical output end of the electro-optic modulator (2); the lengths of the upper arm waveguide (42) and the lower arm waveguide (43) are the same, one end of the upper arm waveguide and one end of the lower arm waveguide are respectively connected with the output end of the input waveguide (41), the other end of the upper arm waveguide and the other end of the lower arm waveguide are respectively connected with the input end of the output waveguide (44), and a microcavity installation space is formed between the upper arm waveguide and the lower arm waveguide; The output end of the output waveguide (44) is connected with the input end of the first beam splitter (5); The micro-ring cavity waveguide (45) is arranged in the micro-cavity installation space, is respectively in non-contact coupling with the upper arm waveguide (42) and the lower arm waveguide (43), and is used for generating double comb beams through a four-wave mixing effect; The first output end of the first beam splitter (5) is connected with the spectrum monitoring unit, the second output end of the first beam splitter is used for being connected with the input end of a target to be detected, the generated double-comb light beam is divided into a monitoring light beam and a testing light beam, the monitoring light beam is output from the first output end, and the testing light beam is output from the second output end.
  5. 5. The frequency-stabilized phase-locked mid-infrared single-cavity double-comb measuring system as claimed in claim 4, wherein the spectrum monitoring unit is a spectrum analyzer (6); The amplifying beam splitting unit comprises an optical fiber amplifier (7) and a second beam splitter (8); The spectrum analyzer (6) is connected with a first output end of the first beam splitter (5) and is used for monitoring the spectrum characteristics of the monitoring light beam; The input end of the optical fiber amplifier (7) is used for being connected with the output end of the target to be detected, and the output end of the optical fiber amplifier (7) is connected with the input end of the second beam splitter (8) and is used for carrying out power amplification on double comb beams output by the target to be detected; The first output end of the second beam splitter (8) is connected with the input end of the homodyne extraction unit, the second output end of the second beam splitter is connected with the input end of the power balancing unit, and the second output end of the second beam splitter is used for dividing the double-comb beam amplified by power into a reference beam and an original beam, the reference beam is output from the first output end, and the original beam is output from the second output end.
  6. 6. The frequency-stabilized phase-locked mid-infrared single-cavity double-comb measuring system as claimed in claim 5, wherein the homodyne extraction unit is a filter (9); the power equalization unit is a power attenuator (10); the input end of the filter (9) is connected with the first output end of the second beam splitter (8), and the output end of the filter is connected with one input end of the double-comb detection unit and is used for carrying out narrow-band filtering on double combs of the reference beam so as to extract a common zero-frequency offset signal; The input end of the power attenuator (10) is connected with the second output end of the second beam splitter (8), and the output end of the power attenuator is connected with the other input end of the double-comb detection unit and is used for carrying out power tuning on the double combs of the original light beam so as to balance power difference.
  7. 7. The frequency-stabilized phase-locked mid-infrared single-cavity double-comb measuring system as claimed in claim 6, wherein the double-comb detecting unit is a balance detector (11); the signal analysis unit is a spectrum analyzer (12); two input ends of the balance detector (11) are respectively connected with the output end of the filter (9) and the output end of the power attenuator (10), and the output end of the balance detector (11) is connected with the input end of the spectrum analyzer (12); The balance detector (11) is used for carrying out balance detection on the reference beam and the original beam so as to eliminate zero frequency offset and realize conversion from optical frequency to radio frequency of the double combs; The spectrum analyzer (12) is used for measuring beat frequency signals of the double combs.
  8. 8. The frequency-stabilized phase-locked mid-infrared single-cavity double-comb measurement system according to any one of claims 4-7, wherein the micro-ring cavity waveguide (45) is circular or racetrack-shaped; The electro-optical modulator (2), the input waveguide (41), the upper arm waveguide (42), the lower arm waveguide (43), the output waveguide (44) and the micro-ring cavity waveguide (45) are integrally arranged and are all made of lithium niobate.
  9. 9. The method for measuring the mid-infrared single-cavity double-comb with the frequency stabilization phase lock is characterized by comprising the following steps of: Step 1, connecting a target to be measured to the frequency-stabilizing phase-locked mid-infrared single-cavity double-comb measuring system in any one of claims 1 to 8; Step 2, starting a pumping laser unit and a sideband generating unit, and adjusting the sideband generating unit until the spectrum monitoring unit monitors two new frequency comb teeth; Step3, adjusting the pumping laser unit until the spectrum monitoring unit monitors that the wide spectrum double comb is generated; step 4, adjusting the homodyne extraction unit to enable the homodyne extraction unit to have only one pair of double-comb frequency components in the wide-spectrum double-comb in the light transmission range; And 5, adjusting the power balancing unit until the signal analysis unit measures a double-comb measurement result of the target to be measured.
  10. 10. The frequency-stabilized phase-locked mid-infrared single-cavity double-comb measurement method of claim 9, wherein the method is characterized by: Step 2, a single-frequency laser (1) and an electro-optical modulator (2) are started, and the output frequency of a microwave driving signal output by a microwave generator (3) is regulated until two new frequency comb teeth uniformly distributed on two sides of the center wavelength can be observed on a spectrum analyzer (6), wherein the output frequency of the microwave generator (3) is identical to or integral multiple of the repetition frequency of a micro-ring cavity waveguide (45), which indicates that the initial generation of an optical frequency sideband required by double-comb low-threshold excitation is completed; step 3, adjusting the driving voltage and current of the single-frequency laser (1), increasing the output power of the pumping laser, and adjusting the wavelength of the pumping laser until stable wide-spectrum double-comb generation can be observed on the spectrum analyzer (6), which indicates that the pumping laser frequency is consistent with the resonance frequency of the micro-ring cavity waveguide (45); step 4, specifically, a filter (9) is regulated to enable the light transmission range of the filter to have only one pair of double-comb frequency components in the wide-spectrum double-comb; And 5, specifically, tuning the power attenuator (10) until the intensity of the double-comb beat frequency signal measured by the spectrum analyzer (12) reaches the highest, wherein the radio frequency result observed by the spectrum analyzer (12) and detected by the balance detector (11) is the double-comb measurement result of the target to be measured.

Description

Frequency-stabilizing phase-locked mid-infrared single-cavity double-comb measuring system and method Technical Field The invention relates to a system and a method for measuring a middle infrared double comb, in particular to a system and a method for measuring a middle infrared single-cavity double comb with frequency stabilization and phase locking. Background The double-comb measuring technology performs cooperative work through two optical frequency combs with tiny repeated frequency difference, can utilize a pulse sequence to perform equivalent deceleration sampling on echoes in a time domain, finely restore waveforms and extract flight time, and the frequency domain can convert optical frequency down to a radio frequency band capable of accurately detecting through beat frequency among comb teeth, so that the double-comb measuring technology is one of the most precise measuring technologies mastered at present. By means of the unique advantages of synchronous fusion of time-frequency domain limit characteristics, great potential is shown in a plurality of fields, particularly in the tip scenes of equipment manufacture, space detection, spectrum analysis and the like, long-range nanoscale absolute distance dynamic measurement and microsecond ultra-high resolution spectrum measurement can be realized, and the problem that the traditional laser interference scheme faces the problem that the measurement speed and the measurement precision are difficult to be compatible is solved. However, the conventional double-comb system is constructed by means of two sets of independently operated mode-locked lasers, and has a complex structure and high manufacturing cost, so that the conventional double-comb system is basically large-scale precision equipment in laboratory level, and the practical range is severely limited. More importantly, the high-precision double-comb measurement has extremely high requirements on the stability and the coherence of two sets of optical frequency combs, and strict repetition frequency stabilization and initial phase locking (namely frequency stabilization phase locking) are usually required to be carried out on the optical frequency combs, so that noise is greatly suppressed, and the measurement capability limit is improved. According to the optical basic principle, any two of the three parameters of the absolute frequency (f 0), the repetition frequency (f rep) and the carrier envelope phase offset frequency (f ceo, also called zero frequency offset) of the center or a certain comb tooth of the optical comb are required to be subjected to fine feedback control, so that frequency stabilization phase locking can be completed, and the ultra-stable operation of the optical frequency comb is realized. For the locking of f 0, a common means is to filter out one comb tooth of the optical comb and lock it to a very fine reference frequency (such as an ultra-fine ultra-stable cavity or a molecular frequency stabilized laser), wherein the locking process needs to perform beat frequency detection on the target comb tooth and the reference laser, and then perform power or wavelength feedback control on the pump laser by a high-speed servo system (such as a broadband phase-locked loop) through a real-time error signal. For the stabilization of f rep, the common means is to directly detect the repetition frequency of the optical comb, accurately count and reference the repetition frequency (for example, after a high-precision microwave counter is adopted, then the repetition frequency is compared with ultra-stable microwave frequency sources such as a rubidium clock, a hydrogen clock or a Beidou signal, and the like), and then finely regulate and control the total cavity length of the optical comb through a piezoelectric or temperature control closed loop control system, so that the feedback tuning of the repetition frequency is realized. For f ceo stabilization, the common means is a f-2f or 2f-3f self-reference method, through performing secondary spectrum expansion and power amplification on an optical frequency comb, extracting long wave target comb teeth (2 f or 3 f) of the optical frequency comb, performing frequency multiplication, then performing beat frequency with short wave comb teeth (1 f or 2 f) to obtain f ceo, and then using the f ceo as an error feedback signal of the optical comb system so as to perform stable feedback regulation and control on the power or frequency of a pumping light source. Therefore, in order to realize the frequency stabilization phase locking of the optical frequency comb, the ultra-stable external optical or microwave frequency reference, the broadband servo locking control of the pumping frequency/power, the accurate repetition frequency detection and the real-time feedback tuning of the cavity length, the high nonlinear broadband spread spectrum, the low-noise power amplification and other unit structures are generally needed, so that the overal